1. Field of the Invention
The present invention relates generally to methods and apparatus for dissipating the heat generated by high speed computer chips. More particularly, the invention relates to improved methods and apparatus for dissipating the heat generated by such semiconductors (bare die or chip) through the use of a heat path from the semiconductor to a heat exchanger, wherein the path includes a conductive cooling cup module. The improved methods and apparatus maximize the thermal conductance and heat spreading ability of the heat path, provide electrical isolation for the semiconductor and compensate for the coefficients of thermal expansion of the components in the disclosed heat transfer and dissipation system.
2. Description of the Related Art
High speed computer chips that are used to support present day chip onboard technology emit a great deal of heat. The prior art is replete with heat exchange methods and apparatus that are useful in performing the needed cooling function for such chips.
But a few examples of the variety of cooling and heat transfer mechanisims used in conjunction with semiconductors are those taught in patents to Spaight, U.S. Pat. No. 4,092,697, issued May 30, 1978; Wessely, U.S. Pat. No. 4,517,624, issued May 14, 1985; Wakalayashi et al, U.S. Pat. No. 4,535,384, issued Aug. 13, 1985; Kaufman, U.S. Pat. Nos. 4,546,410 and 4,546,411, issued Oct. 5, 1985; Kirby, U.S. Pat. No. 4,563,725, issued Jan. 7, 1986; and Nilsson, U.S. Pat. No. 4,573,103, issued Feb. 25, 1986.
Designs using thermal compounds (in a variety of ways), pressure (to push packages against cold plates) with resilient material buffers, specially designed heat sinks attached to chips, cooling fins, etc., are all shown in the above referenced patents and form a background for the present invention.
U.S. Pat. No. 4,546,409, issued on Oct. 8, 1985 to Yoshino et al; IBM, in an article by S. Oktay, B. Dessauer and J. L. Horvath, entitled "New Internal and External Cooling Enhancements for the IBM 4381 Module", published by the IBM General Technology Division, East Fishkill, Hopewell Junction, N.Y., 12533; and Mitsubishi Electric Corp., in an article by M. Kohara, S. Nakao, K. Tsuutsumi, H. Shibita, and H. Nakata, entitled "High Thermal Conduction Module", published by the IEEE in 1985, also show specific techniques for performing the aforesaid cooling function. These techniques will be described in more detail since the present invention will be shown to make distinct improvements over these techniques per se.
Yoshino teaches a device for cooling semiconductor elements constituted by an aluminum (or aluminum alloy) cooling plate and a semiconductor element-mounting sheet (made of aluminum or aluminum alloy) where the sheet has on one surface a metal layer to which solder can be applied and the other surface of the sheet is secured, by ultrasonic welding, to a recessed protion of the cooling plate. The Yoshino patent specifically depicts a cup type device that is used as an interface between a diode and the aluminum cooling plate.
In fact, the Yoshino "cup" does not act as a container for thermal compound during operation. The compound is rigidly soldered to the cup and the semiconductor being cooled is rigidly implanted in the solder. The rigidity in the Yoshino system does not allow for different thermal coefficients in the thermal path between the cold plate, heat spreader and the semiconductor. Those skilled in the art will readily appreciate that it would be desirable to overcome this shortcoming of the Yoshino cooling system.
The IBM reference teaches air cooling the chips for its 4381 computer by providing a specially fabricated thermopaste to couple the bare chip to a pedestal which is connected to a heat exchanger. The IBM system has no heat spreading capability which unduly limits the surface area over which heat is transferred. This has a negative effect on the cooling systems ability to conduct heat.
The Mitsubishi reference teaches cementing a copper plate to the bare chip which spreads the heat over a wider area. The copper plate is spaced from the heat exchanger to maintain electrical isolation and heat is conducted across the gap between the two by hydrogen gas. A high degree of manufacturing tolerance is required to provide a reliably small gap.
The lack of heat spreading capability in the IBM teaching and the manufacturing tolerances required in the Mitsubishi teaching further typify shortcomings in the known art.
It would be desirable if a departure from the known art were achieved wherein the thermal conductance from a semiconductor (bare die or chip) to a heat exchanger could be maximized, electrical isolation of the semiconductor could be maintained without negatively impacting manufacturing tolerances of the cooling system and the problems associated with mismatches in coefficients of thermal expansion could be avoided.
Achieving these objectives and placing a greater emphasis on thermal management generally becomes even more important when a bare die (no package) is placed directly on a printed circuit board. As denser packing schemes evolve and power requirements rise, the need for effective cooling design and thermal management increases.